High Temperature Heap Bioleaching Process

ABSTRACT

A heap is constructed with hypogenic copper sulfide bearing ore to include exposed sulfide mineral particles at least 25 weight % of which are hypogenic copper sulfides. The concentration of the exposed sulfide mineral particles is such that the heap includes at least 10 Kg of exposed sulfide sulfur per tonne of solids in the heap. At least 50% of the total copper in the heap is in the form of hypogenic copper sulfides. A substantial portion of the heap is heated to at least 50° C. The heap is inoculated with a thermophilic microorganism, and bioleaching is carried out so that sufficient sulfide mineral particles in the heap are biooxidized to oxidize at least 10 Kg of sulfide sulfur per tonne of solids in the heap and to cause the dissolution of at least 50% of the copper in the heap in a relatively short period of time.

The present application is a continuation of U.S. patent applicationSer. No. 10/964,208, filed Oct. 12, 2004, now pending, which is acontinuation of U.S. patent application Ser. No. 10/086,647, filed Feb.28, 2002, now U.S. Pat. No. 6,802,888, which is a continuation of U.S.patent application Ser. No. 09/650,319, filed Aug. 29, 2000, nowabandoned, which is a continuation-in-part of U.S. patent applicationSer. No. 09/212,579, filed Dec. 14, 1998, now U.S. Pat. No. 6,110,253,all of which are hereby incorporated by reference as if fully set forthherein.

FIELD OF THE INVENTION

The present invention relates to the extraction of copper from hypogeniccopper sulfide bearing ores and concentrates.

BACKGROUND

Hypogenic copper sulfides are an economically important sources ofcopper. Hypogenic deposits are formed by ascending solutions carryinghigh levels of metal ions at fairly high temperatures (up to 500° C.).As these solutions cool, metal sulfides are deposited as crystallizedore minerals as the solutions move up toward the Earth's surface. As aresult, hypogenic deposits are characterized by metal sulfide bearingveins or irregular masses formed within fractures in the country rock.Within these hypogenic deposits, a variety of hypogenic copper sulfidesmay be found depending on the chemical composition of the ascendingsolution. Some of hypogenic copper sulfides found in hypogenic depositsare chalcopyrite, bornite, enargite, tetrahedrite, and tennatite.Hypogenic copper sulfides are also sometimes referred to as primaryenriched copper sulfide minerals. The ascending solutions may alsoeventually reach the surface and appear as hot springs. In thesesituations, the solutions generally become diluted with ground water andthus have lower metal ion levels. As a result, the metal ions in thesehot springs typically precipitate out as metal sulfate salts over time.In addition, the copper sulfide minerals that are formed above the watertable may become altered over time by oxidation to sulfates by thecirculation of air, water, and bacteria. These soluble metal salts aresubsequently carried away in solution by the downward moving groundwater. As the ground water moves to the oxygen deficient lower levels asecondary enrichment can take place. The copper-bearing solutions reactwith the existing chalcopyrite and other hypogenic sulfides such asbornite, enargite, tetrahedrite, and tennatite to form new coppersulfide minerals. The new minerals formed by the descending solutionsare sometimes called supergenic or secondarily enriched copper sulfideminerals. The supergenic copper sulfides—or secondary enriched coppersulfides as they are sometimes referred to—are higher in copper and arecharacterized by the minerals covellite and chalcocite. They are alsomore readily oxidizeable copper sulfide minerals than the hypogeniccopper sulfide minerals. These supergenic copper sulfide minerals aregenerally located below the oxidized zone and the water table and abovethe lower grade of primary sulfide ore.

Chalcopyrite is economically the most important hypogenic copper sulfidemineral, as well as the most economically important source of copperoverall. Presently, smelting technology remains the primary technologyfor recovering copper from chalcopyrite. Smelting chalcopyrite, however,has a number of drawbacks. These include sulfur dioxide gas emissionswhich are environmentally unacceptable, large production of sulfuricacid even though there presently exist only a limited market forsulfuric acid in most areas, and expense. As a result, alternativemethods for recovering copper from chalcopyrite, as well as otherhypogenic copper sulfides, that are more environmentally friendly andless expensive have been sought for a number of years.

A number of alternatives that have been investigated for recoveringcopper from chalcopyrite and its ores have included hydrometallurgicalprocesses. Hydrometallurgical processes have long been used to recovercopper from oxide ores. These processes typically involve sulfuric acidleaching of the oxide ore, copper separation from the pregnant leachliquor by solvent extraction techniques and recovery of metallic copperfrom the strip liquor by electrowinning. These techniques have not onlydemonstrated an ability to recover copper at a competitive costadvantage over most smelting processes, but the electrowon copperproduced in such processes is also now fully competitive in terms ofquality with electrorefined copper produced by the known smelting andrefining techniques. Presently, however, a commercially viablehydrometallurgical process for the recovery of copper from chalcopyrite,and other commercially important hypogenic copper sulfide minerals, hasremained elusive despite extensive research efforts to develop such aprocess. The development of a hydrometallurgical process for the directleaching of chalcopyrite either by chemical or biological means has beencontinuously sought for more than twenty years.

The direct leaching of chalcopyrite and other hypogenic copper sulfideminerals in sulfuric acid solution poses a variety of problems. Attemperatures below the melting point of sulfur (approximately 118° C.),the rate of copper dissolution has, to date been uneconomically slow. Attemperatures above the melting point of sulfur the chalcopyrite andother hypogenic copper sulfide minerals are passivated by what isbelieved to be a layer of elemental sulfur which forms over theunreacted sulfide particles. This again renders the extraction of copperuneconomical by this process. Other leaching systems that have beenstudied over the years for the extraction of copper from chalcopyrite onlaboratory or pilot scale include systems employing concentratedsolutions of ferric chloride or ammoniacal ammonium as lixiviants.

Efforts to bioleach chalcopyrite and other hypogenic copper sulfides ona commercial scale have also proven unsuccessful to date. Hypogeniccopper sulfides such as chalcopyrite are notoriously difficult tobioleach even though bioleaching is now used as the principal productionapproach to extract copper from supergenic copper sulfide minerals suchas chalcocite and covellite at several mining operations around theworld.

Stirred tank and heap biooxidation processes that have employedmesophiles, such as Thiobacillus ferrooxidans, the most commonly usedmicroorganism for biooxidizing sulfide minerals, have largely beenunsuccessful due to the slow leach kinetics of chalcopyrite and otherhypogenic copper sulfides. The slow leach kinetics and incompletebiooxidation of chalcopyrite and other hypogenic copper sulfides areoften attributed to the formation of an inhibiting or passivation layerthat forms on the surface of these copper sulfides as they oxidize. Anumber of different additives have been used in an attempt to increasethe dissolution of copper from chalcopyrite, presumably by disruptingthe passivating layer. These additives include metal salts such asAg₂SO₄, Bi(NO₃), graphite and other sulfide minerals. Anybiohydrometallurgical process for treating hypogenic copper sulfidessuch as chalcopyrite, therefore, will have to address the problem ofthis surface layer. Studies of the problem have led to several theoriesconcerning the nature of the inhibiting layer.

One theory is that a jarosite coating forms on the surface of hypogeniccopper sulfides as they are leached. Jarosite is formed in the presenceof sulfate and ferric iron, in environments in which the pH increases toabove about 1.8. However, high concentrations of jarosite constituentmolecules (sulfate, ferric iron, ammonium or potassium) will lead tojarosite formation at lower pH. The presence of jarosite in analysis ofbioleached chalcopyrite supports this theory. However, experimentsperformed by the present inventors that show slow leaching even at lowconstituent molecule concentration and low pH, as well as reports in theliterature, contradict this theory.

Another theory is that elemental sulfur produced during bioleachingforms a thick blanket that excludes bacteria and chemical oxidants fromthe surface of the hypogenic copper sulfide minerals. The detection oflarge amounts of sulfur in bioleached chalcopyrite supports this theory.In addition, many electron micrographs have shown a thick sulfur coatingon leached chalcopyrite. This theory, however, does not adequatelyexplain why other metal sulfides that also form sulfur when leached donot leach as slow as chalcopyrite.

A third theory proposes that the inhibition is caused by the formationof an intermediate sulfide passivation layer. It is believed that thispassivation layer is less reactive than the original hypogenic coppersulfide and may also inhibit the flow of electrons and oxidants to andfrom the hypogenic copper sulfide. The exact nature of this passivationlayer is complex and is the subject of scientific debate. However, thereis good agreement among the data in the literature that the passivationlayer is unstable at higher temperatures. For example, it has been foundthat temperatures above about 60° C. are high enough to minimize thepassivation of chalcopyrite during leaching.

Experiments with leaching at higher temperatures by both chemical andbiological means have shown accelerated leaching of chalcopyrite.Chemical leaching done at over 100° C., however, requires expensivepressure reactors. Biological leaching is limited to the temperaturelimits of microorganisms that are capable of oxidizing metal sulfides oroxidizing ferrous to ferric. Some examples of microorganisms capable ofoxidizing ferrous, metal sulfides, and elemental sulfur in environmentsabove 60° C. include: Acidianus brierleyi, Acidianus infernus,Metallosphaera sedula, Sulfolobus acidocaldarius, Sulfolobus BC, andSulfolobus metallicus. However, there are also other extremethermophiles that can grow and leach metal sulfides at temperaturesabove about 60° C.

Stirred tank processes utilizing thermophiles have resulted in fasterbioleaching of chalcopyrite than those using mesophiles have or moderatethermophiles have. Indeed, various microorganisms have been used instirred tank processes to leach chalcopyrite concentrate in less than 10days leaching time. However, the high temperature required for rapidleaching of chalcopyrite, as well as other hypogenic copper sulfides,increases the mass transfer limitations of oxygen and carbon dioxide inthe system. This in turn has placed severe limitations on the pulpdensity that can be used in these stirred tank processes due to the highoxygen requirements of the thermophiles and the oxidation reactionoccurring on the surface of the chaleopyrite during leaching. Thus, eventhough the bioleaching process can be completed in less than 10 days ina stirred tank process, the high operating and capital costs associatedwith operating a plant at the low pulp densities necessary to satisfythe oxygen requirements of the system have prevented the commercialimplementation of stirred tank bioleaching for chalcopyriteconcentrates, as well as for concentrates of other hypogenic coppersulfides.

If an effective heap bioleaching process could be developed forhypogenic copper sulfides, such as chalcopyrite, it would have thepotential of operating at a lower cost than tank bioleaching ofconcentrate or pressure leaching of either concentrate or ores ofhypogenic copper sulfides. Thus, heap leaching of hypogenic coppersulfides would be the preferred low cost procedure if a process could bedeveloped to extract a high percentage of the copper in a matter ofmonths. The use of thermophiles in a pilot scale heap leaching processis reported in Madsen, B. and Groves, R., Percolation Leaching of aChalcopyrite-Bearing Ore at Ambient and Elevated Temperatures withBacteria, 1983, Bureau of Mines. However, the process described in thispaper was unable to achieve satisfactory recoveries in a reasonablyshort period of time and thus is not commercially viable. There havealso been other reports of heap bioleaching processes reachingtemperatures above 60° C. However, these too have not been commerciallyviable for extracting copper from. chalcopyrite ores. The failings ofall the reported heap bioleaching processes for chalcopyrite ores isthat they have all generally taken over one year to leach and recoverless than 50% of the copper in the chalcopyrite. The reasons for thisare not entirely clear. However, the present inventors have determinedthat there are several factors that have acted together to preventsuccessful heap bioleaching of chalcopyrite ore. The first is that theheaps that have eventually reached a temperature of 60° C. or higherhave taken a long time to build up enough heat to reach such hightemperatures. As a result, once a temperature of 60° C. is reached, theamount of exposed sulfide mineral particles in the heap is insufficientto maintain the temperature to complete copper leaching. Furthermore, inthe case of larger ore particles, such as those over about 2.5 cm, notenough of the copper sulfides in the ore are exposed to the leachingsolution to permit adequate recoveries. Finally, the high temperaturescan also increase the amount of ferric ion that precipitates asjarosite, which can further slow the leaching.

SUMMARY OF THE INVENTION

The present invention is directed to a high temperature bioleachingprocess for extracting copper from hypogenic copper sulfide bearingores. More particularly, the present invention is directed to providinga high temperature bioleaching process for extracting at least 50% ofthe copper from a heap comprising hypogenie copper sulfide bearing orein a period of about 210 days or less.

As used herein, hypogenic copper sulfide bearing ores will be understoodto refer to cruched ores, tailings and concentrates containing one ormore hypogenic copper sulfide minerals, such as chalcopyrite, bornite,enargite, tetrahedrite, and tennatite. Chalcopyrite ores will beunderstood to refer to crushed ores, tailings, and concentratescontaining chalcopyrite.

A process according to one aspect of the present invention forextracting copper from hypogenic copper sulfide bearing ores comprisesthe steps of: a.) constructing a heap comprising hypogenic coppersulfide bearing ore, the heap including exposed sulfide mineralparticles at least 25 weight % of which comprise hypogenic coppersulfides, wherein the ation of exposed sulfide mineral particles in theheap is such that the heap contains at least 10 Kg of exposed sulfidesulfur per tonne of solids in the heap, and wherein at least 50% of thetotal copper in the heap is in the form of hypogenic copper sulfides;b.) heating a substantial portion of the heap to a temperature of atleast 50° C.; c.) inoculating the heap with a culture comprising atleast one thermophilic microorganism capable of biooxidizing sulfideminerals at a temperature above 50° C.; d.) irrigating the heap with aprocess leach solution comprising sulfuric acid and ferric iron; e)bioleaching sufficient sulfide mineral particles in the heap to oxidizeat least 10 Kg of sulfide sulfur per tonne of solids in the heap and tocause the dissolution of at least 50% of the copper in the heap into theprocess leach solution in a period of 210 days or less from completionof the heap; and f.) collecting a pregnant process leach solution thatcontains dissolved copper as it drains from said heap.

Preferably, a substantial majority of the heat required to initiallyheat the heap to temperature and to maintain the heap at temperature isderived from the bioleaching of sulfide minerals contained within theheap.

In another aspect of the present invention, a high temperature heapbioleaching process for recovering copper from hypogenic copper sulfidebearing ores is provided. The process according to this aspect of theinvention comprises the steps of: a.) constructing a heap comprisinghypogenic copper sulfide bearing ore, the heap including exposed sulfidemineral particles at least 25 weight % of which comprise hypogeniccopper sulfides, wherein the concentration of exposed sulfide mineralsin the heap is such that the heap includes at least 10 Kg of exposedsulfide sulfur per tonne of solids in the heap, and wherein at least 50%of the total copper in the heap is in the form of hypogenic coppersulfides; b.) heating at least 50% of the heap to a temperature of atleast 60° C.; c.) maintaining at least 50% of the heap at a temperatureof at least 60° C. until at least 50% of the copper in the heap isdissolved; d.) inoculating the heap with a culture comprising at leastone thermophilic microorganism capable of bioleaching sulfide mineralsat a temperature above 60° C.; e.) irrigating the heap with a processleach solution at a rate of at least 72 liters/m²/day; f.) bioleachingsulfide mineral particles in the heap, wherein sufficient sulfideminerals are oxidized in a bioleaching period of 210 days or less tooxidize at least 10 Kg of sulfide sulfur per tonne of solids in the heapand cause the dissolution of at least 50% of the copper in the heap intothe process leach solution; g.) collecting a pregnant process leachsolution that includes copper cations as it drains from the heap duringthe bioleaching period; and h.) recovering copper from. the pregnantprocess leach solution.

The above aspects and other objects, features and advantages of thepresent invention will become apparent to those skilled in the art fromthe following description of the preferred embodiments taken togetherwith the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a process flow chart according toone embodiment of the present invention.

FIGS. 2A-2D illustrate another method of practicing the presentinvention.

FIG. 3 is a chart illustrating the estimated percent of copper and ironleached for Example 1 which illustrates certain principles of thepresent invention.

FIG. 4 is a chart illustrating the estimated percent of copper and ironleached for Example 2 which illustrates certain principles of thepresent invention.

FIG. 5 is a chart illustrating the estimated percent of copper and ironleached for comparative Example 3.

FIG. 6 is a chart illustrating the estimated percent of copper and ironleached for Example 4 which illustrates certain principles of thepresent invention.

FIG. 7 is a chart illustrating the estimated percent of copper and ironleached for Example 5 which illustrates certain principles of thepresent invention.

FIG. 8 is a chart illustrating the estimated percent of copper and ironleached for Example 6 which illustrates certain principles of thepresent invention.

FIG. 9 is a chart illustrating the estimated percent of copper and ironleached for Example 7 which illustrates certain principles of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention improves the heap bioleaching of hypogenic coppersulfides by providing a method of accelerating the rate of bioleachingin the heap and increasing the percentage of copper leached from theheap. The introduction of an adequate fuel value into the heap duringthe heaps' construction is an important aspect of the high temperatureheap bioleaching process of the present invention. The fuel componentcan be in the form of hypogenic copper suflides, pyrite, supergeniccopper sulfides and other sulfide minerals that generate a large amountof heat energy when biooxidized. Hypogenic copper sulfides that may beincluded in the heap include, for example, chalcopyrite, bornite,enargite, tetrahedrite, and tennatite. Supergenic copper sulfides thatmay be included in the heap include, for example, chalcocite andcovellite.

The heat is generated by the exothermic oxidation reactions that occurduring biooxidation of these fuel values. A significant portion of thesulfide fuel material, therefore, must be exposed to the air, water, andbiooxidizing microorganisms or ferric ion within the heap to ensure thatan adequate amount of heat can be generated in a sufficiently shortperiod of time to supply a substantial portion of the heat required tomaintain the heap at a temperature above about 50° C. while thehypogenic copper sulfides in the heap are bioleached.

If sufficient fuel values are not present, the heap cannot be maintainedat a temperature above 50° C. while biooxidation of the hypogenic coppersulfides proceeds without providing substantial amounts of heat from anexternal source, which would make the process economically prohibitive.The process will typically be economical if the exposed sulfide mineralsin the heap, that is those sulfide mineral particles that can bebiooxidized in a period of about 210 days or less, contain at least 10Kg of sulfide sulfur per tonne of solids in the heap. In other words,the heap should contain at least 10 Kg of exposed sulfide sulfur pertonne of solids in the heap. This concentration of sulfide sulfurtranslates to a heat value of approximately 50,000 Kcal/tonne of solidsupon oxidation. This is based on the fact that the standard free energychange for the oxidation of pyrite by the reaction in accordance withequation (1):FeS₂+3.5O₂+H₂O→Fe²⁺+2SO₄ ²⁻+2H⁺  (1)is approximately 1440 KJ. Furthermore, although the standard free energychange for the various other sulfide minerals is different, because theheat of formation of each mole of SO₄ ²⁻ accounts for the majority ofthe change in standard free energy for all of these reactions, one canassume that the change in standard free energy for the oxidationreactions of the other sulfide minerals is approximately the same. Itcan be assumed, therefore, that for each mole of S₂ oxidized,approximately 1440 KJ of energy will be released. Thus, if a heapcontains 1% by weight sulfur in exposed sulfide minerals, or 10 Kg ofexposed sulfide sulfur per tonne of solids, it contains a potentiallyuseful fuel value of approximately 50,000 Kcal per tonne of solids inthe heap.

Obviously the higher the concentration of exposed sulfide mineralscontained within the heap the greater the potentially useful fuel valueof the heap will be and the less heat that will need to be supplied byan external source. If the concentration of exposed sulfide minerals inthe heap is sufficiently high, the fuel component of the heap will besuch that the heat generated upon oxidation will be sufficient to heatthe heap to a temperature above 50° C. and to maintain the heap above50° C. while biooxidation of the hypogenic copper sulfides proceeds.

A high temperature heap bioleaching process for extracting copper fromhypogenic copper sulfide bearing ore according to the present inventionis schematically illustrated in FIG. 1. According to the process, a heap20 is constructed with a hypogenic copper sulfide bearing ore, such as achalcopyrite bearing ore. It is desirable for heap 20 to be at least 2.5m high and at least 5 m wide so that the outer extremities of the heapwill help insulate the inner portions of the heap. Typically heap 20will have larger dimensions to make the processes as economical aspossible. For example, heap 20 will typically have a height of at least3 m and a width of at least 10 m. The length of heap 20 will typicallydepend on the limitations of the site on which the heap is constructed,but generally heap 20 will be substantially longer than it is wide.

Although the foregoing dimensions have been provided as guidelines,those skilled in the art will recognize that the dimensions of heap 20can vary significantly. Furthermore, the heap does not have to berectangular as illustrated in FIG. 1, but can also be circular or anyother shape desired or perhaps required by the limitations of the siteat which the process will be carried out.

When completed, heap 20 will generally contain at least 4% by weightwater. Preferably heap 20 will include 7% or more water by weight.However, the more water contained within heap 20, the greater the amountof heat required to heat heap 20 to a temperature above about 50° C.where active biooxidation of the hypogenic copper sulfides in the heapbegins. For example, a heap that contains 7% water by weight will takeapproximately 3,500 Kcal of heat to heat the water in the heap from 20°C. to 70° C. for each tonne of solids in the heap. Whereas a heap thatcontains 10% water by weight will take approximately 5,000 Keal of heatto heat the water in the heap from 20° C. to 70° C. for each tonne ofsolids in the heap. Moreover, the specific heat of water is greater thanthat of ore. Thus, it is desirable to maintain the water content of theinitial heap at a level that does not exceed about 15% water by weightof solids in the heap. Water can be added to the heap during formationof the heap or following completion of the heap while conditioning it inpreparation for the bioleaching process.

As noted above, heap 20 must also include exposed sulfide mineralparticles. The concentration of exposed sulfide mineral particles inheap 20 must be such that the heap includes at least 10 Kg of exposedsulfide sulfur per tonne of solids in the heap. To improve theperformance of the present process, however, the concentration ofexposed sulfide mineral particles is preferably such that the heap willcontain at least 30 Kg of exposed sulfide sulfur per tonne of solids inthe heap. With appropriate heap design considerations, as will bediscussed in more detail below, the concentration of exposed sulfidesulfur can reach levels of 40 to 90 Kg per tonne of solids in the heapor even higher. Thus, even more preferably the concentration of exposedsulfide sulfur is at least about 45 Kg per tonne of solids.

As used herein, exposed sulfide mineral particles will be understood tobe those sulfide mineral particles that are exposed to the air, water,and biooxidizing microorganisms or ferric ions within the heap so thatthey can generally be biooxidized within a period of 210 days or less.The sulfide sulfur in these exposed sulfide mineral particles isreferred to as exposed sulfide sulfur for purposes of the presentapplication to distinguish it from other sulfide sulfur that may be inthe heap but due to its occlusion, in gangue material for example, itsfuel value is not available to the heap in a reasonable biooxidationperiod of 210 days or less.

Typically the majority of the exposed sulfide mineral particles withinthe preferred heap designs of the present invention will be finelyground and have a particle size of 250 μm or less, and preferably aparticle size of less than about 107 μm. However, exposed sulfidemineral particles can also be present in larger ore particles that maybe found in the heap. This is because some fraction of the sulfidemineral particles contained within larger ore particles will typicallyreside on the surface, or close enough to the surface, of the oreparticles to permit access of the necessary components for oxidation tooccur, namely air, water, and biooxidizing bacteria or ferric ions,within a period of about 210 days or less. As those skilled in the artwill appreciate, finer ore particles will typically have more exposedsulfide mineral particles than coarser ore particles.

While the exposed sulfide mineral particles in the heaps of the presentinvention will typically include a variety of sulfide minerals. Aminimum of about 25 weight % of the exposed sulfide mineral particles inthe heap should comprise one or more hypogenic copper sulfides.Desirably, at least 25 weight % of the exposed sulfide mineral particlesin the heap is in the form of chalcopyrite. More preferably thehypogenic copper sulfide fraction of the sulfide mineral particles inthe heap is in the range of about 30 to 70 weight %. The remainder ofthe sulfide mineral particles within heap 20 preferably comprises morereadily biooxidizeable sulfide minerals such as pyrite, arsenopyrite,and supergenic copper sulfides, such as chalcocite, and covellite. Theseless recalcitrant sulfide minerals provide an important fuel componentto the heap, which may be used to heat heap 20 up to temperature andhelp maintain the heap at temperature while biooxidation of thechalcopyrite and/or other hypogenic copper sulfides proceeds. Thepresence of these other less recalcitrant sulfide minerals is alsodesirable because they increase the galvanic leaching of thechalcopyrite and other hypogenic copper sulfides in the heap. Thus, inconstructing the heaps of the present invention, it is desirable for atleast a portion of the exposed sulfide mineral particles to comprise oneor more less recalcitrant sulfide minerals such as pyrite, arsenopyrite,covellite, and chalcocite. The invention, however, can be practiced withup to 100% of the sulfide minerals in the heap being one or morehypogenic copper sulfides, such as chalcopyrite, bornite, enargite,tetrahedrite, and tennatite.

Because supergenic copper sulfide minerals such as chalcocite andcovellite can be readily bioleached using mesophiles such asThiobacillus ferrooxidans the present high temperature process is not aseconomically justified for processing these copper sulfide mineralsalone. Accordingly, at least 50% of the copper in heap 20 should be inthe form of one or more hypogenic copper sulfides, such as chalcopyrite,so that hypogenic copper sulfide minerals are the primary source ofcopper in the heap. Preferably at least 80 to 90% of the copper in theheap is in the form of one or more hypogenic copper sulfides to maximizethe amount of recalcitrant copper sulfide mineral material that is beingprocessed in the heap and thus the economic benefit of practicing thepresent invention.

Heap 20 may be produced using any of the techniques known in the art forproducing heaps for leaching so long as the above parameters aresatisfied for the completed heap. By way of example, the heap may beconstructed by stacking run-of-the-mine ore to form a heap. Preferably,however, the ore is crushed to a particle size of 90% passing 2.54 cm.Alternatively, the crushed ore may be agglomerated prior to stacking toimprove air and liquid flow within the heap as is known in the art.Furthermore, a sulfide mineral concentrate may be added to the heap toincrease the potentially useful fuel value of the heap.

A preferred method for forming heap 20 is described in U.S. Pat. No.5,766,930, which is hereby incorporated by reference as if fully setforth herein. U.S. Pat. No. 5,766,930 describes the construction andoperation of large surface bioreactors that are particularly well suitedfor practicing the present invention.

Thus, for example, heap 20 may be constructed by crushing a hypogeniccopper sulfide hearing ore that is to be bioleached, such as arun-of-the-mine chalcopyrite bearing ore, to a particle size that isless than 2.54 cm, and preferably less than 12.7 mm. The fines fraction,for example the fraction that is less than about 3 mm, is then removedto ensure adequate air flow within the final heap. The plurality ofcrushed coarse ore particles are then coated with a concentrate ofsulfide minerals having a particle size of less than 250 μm, andpreferably less than about 107 μm. The concentrate comprises at leastone hypogenic copper sulfide mineral such as chalcopyrite. In addition,the concentrate also preferably contains one ore more less recalcitrantsulfide minerals such as pyrite, arsenopyrite, chalcocite, andcovellite. As described above, however, because all of the sulfidemineral particles in the concentrate are considered exposed sulfidemineral particles, at least 25 weight % of the total sulfide mineralcontent in the concentrate should be in the form of one or morehypogenic copper sulfides. It is desirable, however, for at least 25weight % of the total sulfide mineral content in the concentrate to bein the form of chalcopyrite.

The concentrate may be coated onto the substrates using a variety oftechniques, including the use of a rolling drum or a slurry sprayer. Thethickness of the concentrate coating on the coarse ore is preferablyless than 1 mm to ensure that the microorganisms being used in thebioleaching process have adequate access to all of the sulfide mineralparticles in the concentrate. Thicker coatings will increase thecapacity of the heap bioreactor, but the rate at which the bioleachingprocess advances will likely be slowed due to decreased access of themicroorganisms being used to the underlying sulfide mineral particles inthe concentrate. To make full use of the capacity of the heap bioreactorwhile ensuring adequate microorganism access, the thickness of theconcentrate coating should be greater than about 0.5 mm and less thanabout 1 mm. This will generally translate to a concentrate loading ofapproximately 9 to 30 weight percent. Typically the concentrate loadingon coarse ore will be about 10 to 15% of the weight of the coarse oresubstrates. This is generally enough, however, to create the heatnecessary to raise the temperature of the heap up to the temperatureoptimum for the extreme thermophiles capable of oxidizing iron andbioleaching hypogenic copper sulfide minerals, such as chalcopyrite, attemperatures above 50° C.

By coating the coarse ore with about ten weight percent of achalcopyrite, or other hypogenic copper sulfide concentrate, the coatedore will typically include at least 30 Kg of exposed sulfide sulfur pertonne of ore. It will be appreciated by those skilled in the art,therefore, that the coarse ore should be coated with as much concentrateas possible and the concentrate should include as much sulfide mineralsas possible to maximize the amount of exposed sulfide mineral particlesin the completed heap. For example, if a typical concentrate thatcontains at least 30 weight % sulfide sulfur is coated onto the coarseore at a loading of 10 weight %, the concentrate coated ore will containat least 3% exposed sulfide sulfur, which translates to a potential fuelvalue of approximately 150,000 Kcal/tonne or ore. On the other hand, if15 weight % of the concentrate is coated onto the coarse ore supportthan the heap will contain at least 4.5% exposed sulfide sulfur, whichhas a fuel value of approximately 225,000 Kcal/tonne of ore. Finally, if30 weight percent concentrate can be coated onto the coarse oresubstrates, the heap will contain at least 9% exposed sulfide sulfur, afuel value of approximately 450,000 Kcal/tonne of ore.

The use of uniformly coated coarse ore substrates that have a maximumparticle size of 2.5 cm, and preferably less than 12.7 mm, ensuresadequate exposure of the chalcopyrite mineral in the coarse ore supportmaterial to the oxidizing solutions containing ferric and cupric ionsand to the microorganisms capable of converting ferrous ions to ferricions that aid in the leaching process. Use of coarse support ore that issmaller than 2.5 cm and larger than 3.0 mm also results in a heap designthat permits adequate loading of fuel values in the form of a sulfidemineral concentrate into the heap while ensuring adequate liquid and airflow within the heap and exposure of the sulfide mineral concentrate tothe oxidizing environment of the heap. Therefore, when the concentratecoated coarse ore particles having the above characteristics are stackedto form a heap they provide a very large surface area bioreactor that isvery efficient in terms of bioleaching the coated concentrate. Most ofthe highly exposed sulfide minerals in the concentrate will generallybiooxidize in 30 to 90 days. However, in the case of the mostrecalcitrant mineral sulfides such as chalcopyrite and other hypogeniccopper sulfides, the leaching may be much slower in comparison.

The concentrate of sulfide mineral particles may be produced from thefines generated by crushing the hypogenic copper sulfide ore to a sizeless than 2.5 cm. Typically this will be the portion of the ore that isless than about 3.0 mm. The sulfide mineral particles in this finesfraction can be concentrated from the remainder of the fines byflotation or gravity separation or by a variety of other methodsrecognized by those skilled in the art. Removing the minus 3.0 mmfraction of the ore is beneficial because if too many fines are presentin the heap they can limit the flow of liquid and air within the heap.The fine ore could also consume unacceptable amounts of acid and thuslead to higher pH levels in the heap and more jarosite and ferricprecipitation.

In addition to using the hypogenic copper sulfide concentrate producedfrom the fines fraction of the ore, the coarse ore particles may becoated with hypogenic copper sulfide concentrates produced from othercopper bearing ores. It also may be beneficial to mix in concentrates ofother sulfide minerals with the hypogenic copper sulfide concentrate forthe reasons described above.

Chalcopyrite concentrates made for the smelting process are generallyseparated from other sulfide minerals such as pyrite. The separationprocess can be a variety of methods recognized by those skilled in theart of mineral processing. The general purpose of this separation is toachieve high copper content for the economical smelting of theconcentrate. Concentrates that are high in pyrite, and therefore, lowerin copper are less economical to process by smelting. The separationprocesses used to achieve high concentrations of copper, however,increase the cost of producing copper. They also lower the overallrecovery of copper. This is because the higher the concentration ofcopper one tries to achieve in the concentrate, the more copper thatwill necessarily be lost to the tails of the separation process.

An advantage of the high temperature heap bioleaching process of thepresent invention, therefore, is that the concentrate added to the heapneed not be as high a percentage of copper as is required for economicalsmelting. As described above, the presence of pyrite can accelerate theleaching of the hypogenic copper sulfides, such as chalcopyrite, in thetreated ore through galvanic interactions. Moreover, the biooxidation ofpyrite in the heap also provides a source of heat that can help raiseand maintain the temperature of the heap in a range of 60 to 80° C.,which in turn will promote the growth of extreme thermophiles and thefaster leaching of hypogenic copper sulfides. Therefore, greater overallcopper recoveries from a hypogenic copper sulfide ore body, such as achalcopyrite ore body, can be realized with the present invention whilesimultaneously realizing a cost savings from not having to produce ashigh a grade of concentrate.

Although the heap has been described above as being constructed usingcoarse ore particles as support, other materials may also be used assupport for the concentrate in the present invention. For example, thecoarse support material may be selected from the group consisting ofrock, brick, slag, and plastic. The coarse support may also comprisecoarse ceramic particles. If the support ore is rock, as those skilledin the art will appreciate, a variety of rocks can be used for thecoarse support, including lava rock, barren rock, and crushed copperore.

An advantage of using coarse chaleopyrite or other hypogenic coppersulfide ore particles as the support material is that the hypogeniccopper sulfides contained within this support material can be at leastpartially biooxidized during the process. Furthermore, the coarsesupport material can be recycled a number of times through the processby removing the biooxidized concentrate and recoating it with freshconcentrate, thereby resulting in even higher recoveries of copper fromthe coarse support.

In addition, after the coarse ore support is processed through theprocess one or more times, it can be ground and the remaining sulfideminerals contained therein separated using known techniques in the artto form a sulfide mineral concentrate. This concentrate can then becombined with other concentrate for coating on coarse ore supportmaterial and processing according to the invention.

Barren rock, such as granite, that contains a small amount of carbonatemay be beneficial in helping suppress the amount of iron removed in thepregnant leach liquor. As the carbonate mineral in the rock reacts withthe acid in the process leach solution, it causes local pH increasesresulting in the precipitation of iron. As a result, the concentrationof copper in the final pregnant leach liquor collected from the heap andsent to the solvent extraction plant for copper recovery may be able tobe increased. This is due to the fact that solvent extraction plants cantypically only handle a maximum concentration of about 5 g/l iron in thepregnant leach liquor before special treatments must be performed toselectively remove the iron. Thus, without the precipitation effectcaused by the carbonate mineral in the support rock, the pregnant leachliquor must have lower concentrations of copper than otherwise might bepossible to ensure that the iron concentration does not exceed thelimits of the solvent extraction plant.

Another preferred heap design for practicing the present invention isdescribed in U.S. Pat. No. 5,431,717, which is hereby incorporated byreference. In accordance with this patent, a heap may be constructed byremoving all of the fine material from the hypogenic copper sulfide ore,for example that fraction of ore that is less than about 0.3 cm, andthen adding a hypogenic copper sulfide bearing concentrate to the heap.This can be accomplished by distributing the concentrate on the top ofthe heap so that it migrates down through the heap during bioleaching orsimply mixing it in with the remainder of the ore during heap formationwithout necessarily producing a uniform coating of the concentrate onthe coarse ore prior to heap formation.

To fully utilize the heat generated from the exothermic oxidationreactions that will occur during biooxidation, the heap should beconstructed in such a way to hold in as much heat as possible but alsoallow for the control of temperature so that the temperature optimum forthe biooxidizing microorganisms is not exceeded. This can beaccomplished by covering the heap with an insulating barrier layer 22 tohold in heat and water vapor. Insulating barrier layer 22 may be a tarp,plastic sheets, fiberglass insulation, a layer of crushed rock, or anyof the other insulating barriers known in the art. In the case ofoperations in cold climates it may be preferred that the heap be builtwithin an insulated walled enclosure to aid in maintaining the heat.

In addition to covering the heap, the flow of process leach solutionfrom emitters 24 down through the heap will transport heat from the topof the heap to the bottom of the heap. The movement of air up throughthe heap will transport heat up through the ore. Therefore, if both theflow of liquid and air can be controlled separately, the heat generatedfrom the process can be moved out of the heap either through the top ofthe heap in the form of water vapor or through the bottom of the heap inthe form of hot liquid. Alternatively, the heat of reaction can be heldwithin the heap by balancing the flow of liquid and air.

The heap preferably contains one or more temperature monitoring devicessuch as a thermocouple so that the temperature profile of the heap canbe continuously monitored. The placement of several thermocouplesthroughout the heap would be preferred to best control the temperatureof the heap.

After the heap is constructed, a substantial portion of the heap needsto be heated to a temperature of at least 50° C., preferably at least60° C. and even more preferably at least 70° C. The higher thetemperature of heap 20, the faster the biooxidation of the hypogeniccopper sulfides, such as chalcopyrite, will proceed. By substantial itis meant that ultimately at least 50%, of the heap should reach atemperature at or above the target temperature. Preferably at least 80%of the heap will reach a temperature above the target temperature tomaximize the recovery of copper from the heap and the recovery rate.

Heap 20 should be heated to temperature as quickly as possible. Thiswill help ensure that sufficient exposed sulfide minerals remain in theheap once it reaches temperature to supply the majority, if not all, ofthe heat necessary to maintain the heap at temperature throughout thehigh temperature biooxidation of the hypogenic copper sulfides in theheap. Typically heating the heap to temperature within a period of 45days will be adequate to satisfy this goal. However, heap 20 ispreferably heated to temperature within a period of 30 days or less tominimize the total time for the process to be carried out and tomaximize the concentration of exposed fuel values remaining in the heapfor bioleaching the hypogenic copper sulfides in the heap. As the amountof heat lost from heap 20 is time dependent, increasing heap 20 totemperature as quickly as possible will also help minimize the amount ofheat lost from the heap during the biooxidation process.

The heap may be heated to temperature by a variety of methods. In theevent of heap leaching operations in a cold climate or when insufficientexposed sulfide minerals are available to add to the heap, an externalsource of heat such as hot liquid, steam or hot air may be added to theheap to start the process or to maintain the optimal temperature. Forexample, heated process leach solution may be pumped from reservoirs 26to the top of heap 22 through process leach solution supply lines 28 and30. The process leach solution is then distributed over the top of heap20 through pressure emitters 24. Other means of distributing processleach solution that are known in the art may also be used, includingbagdad wigglers, sprinklers, wobblers, and flooding. The advantage ofpressure emitters is that the amount of water lost due to evaporation isminimized. Furthermore, the portion of supply line 30 that runs alongthe top of the heap may be buried to further reduce evaporation andimprove the insulation of supply line 30 in situations where the processleach solution may be heated.

Alternatively, heap 20 may also be heated by pumping steam or hot airthrough steam or hot air supply line 32 to perforated distribution pipes34 buried in the bottom of the heap. Supply line 32 and perforateddistribution pipes 34 may also supply ambient air for purposes ofincreasing the oxygen and nitrogen levels in the heap as well as toremove heat from heap 20 should it become overheated.

The heap must be inoculated with a culture including at least onethermophilic microorganism capable of bioleaching sulfide minerals at atemperature above 50° C., and preferably above 60° C. This may occurbefore or after the heap reaches temperature, or at any time during thebioleaching process to increase the amount of thermophilicmicroorganisms in the heap.

A process leach solution is also applied to the heap during thebioleaching step, typically at a rate of at least 72 1/m²/day. Theprocess leach solution helps maintain the appropriate conditions withinthe heap for bioleaching the sulfide minerals and carries away thesoluble biooxidation products. In particular, as the copper sulfideminerals are biooxidized, the copper from these minerals is dissolvedinto the process leach solution, forming a pregnant process leachsolution.

Once a portion of the heap reaches at least 50° C., the thermophilicmicroorganisms in that portion of the heap will become active and beginto rapidly bioleach the exposed hypogenic copper sulfide minerals andother sulfide minerals in that region of the heap. This will produceadditional heat which in turn will help increase the temperature ofsurrounding regions in the heap to above 50° C. until ultimately asubstantial portion of the heap is above 50° C., and preferably above60° C. The actual amount of the heap that is heated above the desiredtemperature will depend on the rate at which heat is input into the heapthrough the oxidation of sulfide minerals and through other heatadditions to the heap, and the rate at which heat is lost from the heapthrough convection and radiation.

If bioleaching is carried out so that at least 10 Kg of the sulfidesulfur per tonne of solids in the heap is oxidized in a period of 210days or less from completion of the heap, a significant fraction of theheat required to maintain the heap at temperature while bioleaching thehypogenic copper sulfides in the heap may be obtained from theexothermic oxidation reactions occurring within the heap. Furthermore,by having sufficient exposed sulfide mineral particles within the heapas described above, it is possible to bioleach at least 50% of thecopper sulfide minerals in the heap and thereby cause at least 50% ofthe copper in the heap to dissolve into the process leach solutionwithin a 210 day period from completion of the heap. In appropriatelydesigned heaps, it will be possible to extract at least 70%, andpreferably over 80%, of the total copper in a period of 210 days orless. Indeed, if a sufficient concentration of the hypogenic coppersulfides in the heap are found in particles having a size of less than250 μm, and preferably less than about 107 μm, it will be possible toachieve recoveries of over 80 or 90% in a about 90 to 100 days.

The use of thermophilic chemolithotrophic microorganisms that biooxidizehypogenic copper sulfide minerals, as well as other sulfide minerals,make it possible to operate the heap at temperatures above about 60° C.and speed up the biooxidation rate of the hypogenic copper sulfides inthe heap. These microorganisms are defined as those that live attemperatures in excess of about 60° C., derive their energy frominorganic elements, such as iron and sulfur, and obtain their carbonfrom carbon dioxide fixation. These organisms, represented by suchgenera as Sulfolobus, Acidianus, and Metallosphaera, are actuallyArchaea, but are frequently referred to as bacteria in the literature.

Because thermophilic microorganisms are capable of thriving on mineralsulfides in high temperature environments, these microorganisms areideally suited for the process of the present invention, which requiresthe use of high temperature heap leaching and may employ heap designswith high concentrations of sulfide minerals that result in largeamounts of excess heat.

In addition to biooxidizing sulfide minerals, many thermophilicmicroorganisms also oxidize elemental sulfur and ferrous iron. Byoxidizing elemental sulfur, which is thought to contribute to a blindingof the surface of the chalcopyrite and other hypogenic copper sulfidesduring biooxidation, the use of thermophiles may improve the leach rateof these minerals by minimizing the amount of sulfur that is depositedon their surface during the bioleaching process. By oxidizing ferrousiron to ferric iron, these microorganisms also help maintain a highredox potential within the heap and allow for additional ferric leachingof the sulfide minerals in the heap.

Some examples of thermophilic microorganisms capable of oxidizingferrous, sulfide minerals and sulfur are: Acidianus brierleyi, Acidianusinfernus, Metallosphaera sedula, Sulfolobus acidocaldarius, SulfolobusBC, and Sulfolobus metallicus. These thermophilic organisms are capableof leaching both the hypogenic copper sulfide concentrate and the oresubstrates of the preferred heap design in a period of less than 90 daysat a temperature of 60 to 80° C. Other extreme thermophiles that areknown in the art and that can grow and leach copper sulfides as well asother sulfide minerals within this temperature range may also be used topractice the present invention.

Heap 20 is preferably inoculated with a mixed thermophile culture thatcontains two or more thermophiles. Although these microorganisms allthrive at high temperatures, at low pH, and can utilize mineral sulfidesas energy sources, they differ in such attributes as optimum growthtemperature, affinity for and ability to leach particular minerals, andtolerance of solution components (e.g., salts). Moreover, because theconditions within the heap may vary sufficiently in terms oftemperature, salt concentrations, etc, certain thermophiles may thrivein some regions while others thrive in other regions. Thus, byinoculating with a mixed thermophile culture, the most potent specieswill dominate within the particular bioleach conditions present withinthe heap or a region within the heap, resulting in the best possibleleach.

Only a small fraction, generally less than one percent, of soil microbescan be cultured well in the laboratory. Therefore, by inoculating heapswith only fresh laboratory thermophilic cultures only a small fractionof the possible microorganisms that exist in nature are being tapped. Acontinuously operating high temperature heap, however, will naturallyselect for microorganisms that are best able to bioleach copper sulfideore at high temperatures. Thus, because a large amount of ore and rockthat is used to build each heap will also contain native microbes, theprocess according to the present invention will also automaticallyselect the native microorganisms that have enzymes, as well as othernative biomolecules, that are able to bioleach sulfide minerals at hightemperature. Furthermore, because the solutions and/or support rock arelikely to contain microbes that have not been previously isolated orthat cannot be maintained well in a laboratory culture by existingtechnology, the operating heap will become a source of microbes that arenot currently available from any known culture collections. As a result,the heaps of hypogenic copper sulfide bearing ore that are processed inaccordance with the present invention will provide an excellent sourceof microorganisms for use as an inoculum for starting biooxidation insubsequent heaps that are processed according to the present invention.Previously biooxidized heaps will also provide an excellent source ofmicroorganisms for use as an inoculum in other high temperature heapbiooxidation processes, including, for example, high temperature heapbiooxidation processes for recovering gold and other precious metalsfrom refractory sulfide ores and high temperature heap biooxidationprocesses of base metal sulfide ores.

As noted above, the preferred heap design is one that is over 3 metershigh and 10 meters wide. Heaps of this size will help maximize heatretention in the majority of the heap. This is because the outer mostextremities of the heap will act as a heat insulator for the rest of theheap. Depending on how well the heap is insulated and the outsideenvironment, however, the outer most extremities of the heap may notreach a temperature over 50° C. Inoculating the heap with a combinationof mesophiles and moderate thermophiles will, therefore, aid in thebioleaching of the cooler regions of the heap. Even though the amount ofcopper extraction from these cooler regions will be less than theextraction possible within the higher temperature regions of the heap,the overall extraction of the entire heap will be improved. Thus, in apreferred mode of practicing the present invention, in addition toinoculating the heap with one or more thermophiles, the heap is alsoinoculated with one or more mesophilic and/or one or more moderatethermophilic microorganisms.

In a preferred method of practicing the present invention, a substantialportion of the heat required to initially heat the heap to temperatureis derived from bioleaching sulfide minerals contained within the heap.

If heap 20 contains sufficient exposed readily biooxidizeable sulfideminerals such as pyrite, arsenopyrite, chalcocite, and covellite, thenheap 20 may be heated, at least partially, by utilizing the fuel valuesof these exposed, readily biooxidizeable sulfide minerals. This isaccomplished by inoculating the heap with a culture containing one ormore mesophilic microorganisms capable of biooxidizing sulfide mineralsthat are well known in the art. As biooxidation proceeds, the heatgenerated from the exothermic oxidation reactions of the exposed,readily biooxidizeable sulfide minerals will begin to heat the heap. Asignificant portion of the heat required to heat heap 20 to temperatureof 50° C., or preferably 60° C., may be supplied by biooxidation ifenough sulfide mineral particles are bioleached to oxidize at least 10Kg of sulfide sulfur per tonne of solids in the heap within a period of45 days or less, and preferably 30 days or less. Thus, in order to heatheap 20 using the heat released through the biooxidation of sulfideminerals, heap 20 should be constructed to contain at least one exposedreadily biooxidizeable sulfide mineral in sufficient quantities tosupply the heap with at least 10 Kg of sulfide sulfur per tonne ofsolids.

If the heat released through biooxidation is to be used as the heatsource for heating heap 20 to temperature, then the concentration ofexposed hypogenic copper sulfides in the heap is also preferablysufficient to supply at least 10 Kg sulfide sulfur to the heap. This isso that once the heap is heated to temperature, there will be sufficientsulfide minerals remaining in the heap to help maintain the temperatureabove the target temperature for biooxidation of the hypogenic coppersulfides to proceed over a period of approximately 60 to 150 days.

Heap 20 will typically be heated in a step-wise fashion if the heatreleased through biooxidation is to be used to heat the heap. First, theheap is inoculated with one or more mesophiles that are capable ofbiooxidizing sulfide minerals. It is then inoculated with a culturecomprising one or more moderate thermophiles. Alternatively, theseinoculations may occur simultaneously if desired. Mesophiles typicallyoperate within a temperature range of about 25° C. to 40° C., whilemoderate thermophiles typically operate in a range of about 40° C. to55° C. Thus the mesophiles can be used to heat the heap up to atemperature of about 40° C. Once the heap reaches a temperature of about40° C., the mesophiles will become less active. However, if the heap hasalso been inoculated with moderate thermophiles, these microorganismswill become active as the temperature of the heap approaches about 40°C. The moderate thermophiles can then continue to oxidize the exposedsulfide mineral particles in the heap until a substantial portion of theheap reaches a temperature of about 50° C. to 55° C. where the moderatethermophiles start to become less active. At this point, however, thegrowth of extreme thermophiles is favored. As a result, the extremethermophiles within the heap will become active and begin to oxidizeadditional sulfide minerals in the heap further increasing thetemperature of the heap. At temperatures above about 50° C. andespecially over about 60° C., the rate of biooxidation of the hypogeniccopper sulfide minerals in the heap will rapidly increase due to thefact that the passivation layer that inhibits bioleaching at lowertemperatures tends to degrade at temperatures above about 50° C.

Any of the mesophilic or moderatly thermophilic microorganisms that areknown in the art to be capable of biooxidizing sulfide minerals may beused in the present invention. Examples of mesophiles that may be usedin practicing the present invention include Thiohacillus ferrooxidans,Thiobacillus thiooxidans, Thiobacillus organoparus, Thiobacillusacidophilus, and Leptospirillum ferrooxidans. Examples of moderatethermophiles that may be used in practicing the present inventioninclude Sulfobacillus thermosulfidooxidans, Thiobacillus caldus, andThiobacillus cuprinus.

The heap is irrigated with a process leach solution (PLS) throughout thebiooxidation period. The process leach solution typically includessulfuric acid and iron in ferric and/or ferrous form. The process leachsolution may also contain nutrients to help the biooxidizingmicroorganisms grow. However, the nutrients necessary for themicroorganisms to grow and metabolize the sulfide minerals in the heapmay be present within the ore being bioleached.

The leaching of hypogenic copper sulfides such as chalcopyrite canconsume acid and cause the pH of the heap to increase. The increasing pHcan lead to jarosite formation and ferric precipitation. To prevent thisprecipitation from becoming extensive and retarding the leachingprocess, the process leach solution should be maintained below a pH of1.5, especially once the heap reaches a temperature above 50° C. and thebiooxidation of the hypogenic copper sulfide minerals begins to proceedrapidly. To further minimize the precipitation of ferric and jarosite,the ferric concentration should also be maintained below 3 g/l,especially once the heap is raised to a temperature above about 50° C.The nutrient salts should also be kept low after the temperature of theheap is raised above about 50° C., especially in potassium and inammonium sulfate, both of which can increase jarosite formation. Theaddition of a small amount of chloride (1 to 5 g/l as NaCl) may helpmaintain ferric in solution and enhance leaching of copper over iron.Thus, it may be desirable to use a chloride medium to bioleach the heap,especially after the temperature of the heap is raised above 50° C. If achloride medium is used for the process leach solution, however,thermophilic microorganisms that exhibit chloride resistance should beselected.

The flow rate at which the heap is irrigated with the process leachsolution will depend on a number of factors. Two of the primaryfunctions of the process leach solution are to provide acid and removecopper that has been dissolved during the bioleaching process. As aresult, the peak flows will typically occur at the beginning of theprocess to reduce the pH of the heap to a suitable level that isconducive to the bioleaching process. Once the off solution from theheap is below a pH of about 2.0, preferably about 1.8, the heap isadequately conditioned and appropriate conditions should exist withinthe heap for bioleaching.

The application rate of the process leach solution will also tend to behigher once the heap reaches optimum temperature for hypogenic coppersulfide mineral biooxidation. As the temperature of the heap is raisedto a temperature suitable for biooxidation of hypogenic copper sulfideminerals, the hypogenic copper sulfide minerals in the heap will beginto biooxidize rapidly. Because the biooxidation of hypogenic coppersulfides consumes acid, additional process leach solution will typicallyneed to be added to maintain a low pH environment suitable for furtherbiooxidation. The rate of biooxidation of the hypogenic copper sulfideminerals will tend to be greatest for a period shortly after the heap israised to the optimum temperature. As a result, the application rate ofthe process leach solution will also tend to be high during the periodwhen biooxidation of the hypogenic copper sulfide minerals proceedsrapidly in the heap.

As the copper sulfide minerals in the heap are biooxidized, copper willdissolve into the process leach solution, thereby forming a pregnantprocess leach solution. In determining the appropriate application rateof the process leach solution, therefore, it is also desirable toutilize a flow rate that will ensure a copper concentration of greaterthan 1 g/l, preferably greater than 2 g/l, and even more preferablygreater than 5 g/l. This is particularly true once the biooxidation ofthe hypogenic copper sulfide minerals, which will be the primary type ofcopper sulfide minerals in the heap, begins to proceed rapidly. The flowrate of the process leach solution should be adequate, however, toensure that the final concentration of the ferric iron in the pregnantprocess leach solution is less than 5 g/l and preferably less than 3g/l. While concentrations up to 5 g/l ferric ion may typically behandled in known in the art solvent extraction processes, concentrationsgreater than about 3 g/l will tend to result in excess ferric andjarosite precipitation in the high temperature environment of the heap.

Finally, the flow rate of the process leach solution is preferablyselected to accomplish the foregoing goals with the lowest applicationrate possible. By maintaining the flow rate of the process leachsolution at the lowest possible level to accomplish the foregoing goals,the amount of heat lost from the heap can be minimized, thus minimizingthe potential need for the application of external heat to maintain theheap at the optimal temperature during hypogenic copper sulfide mineralbiooxidation.

With the foregoing goals in mind, the process leach solution willtypically be applied at a rate of at least 72 1/m²/day, and preferablyat a rate of least 144 1/m²/day. For heaps having the preferreddimensions mentioned above, the process leach solution will generally beapplied at a rate of about 300 to 600 1/m²/day.

The application of the process leach solution does not have to becontinuous. The present invention may be practiced with irrigationfollowed by drying or rest periods. While no process leach solution isapplied during the drying period, or dry cycle as it is sometimesreferred to in the art, the heap is not permitted to dry out during thisrest period. Rather, the heap will typically continue to producedrainages throughout the dry or rest period.

As the pregnant process leach solution drains from the heap, it willcollect in drain 35. From drain 35, the pregnant process leach solutionmay be drained by gravity or pumped to reservoirs 26 via pipe 36.Preferably, the pregnant process leach solution is transferred toreservoirs 24 as quickly as possible to minimize heat losses from thepregnant process leach solution. To further minimize heat losses fromthe pregnant process leach solution, reservoirs 24 may be insulated.

Once the concentration of copper in the pregnant process leach solutionreaches a desired level, the pregnant process leach solution is sent toa solvent extraction plant 38 for recovery of copper. The design,construction, and operation of solvent extraction plants are well knownin the art and need not be described further herein. Elemental copper 44may be recovered from the pregnant strip liquor 40 coming out of thesolvent extraction plant using an electrowinning cell 42 as is wellknown in the art. After copper is removed from the pregnant strip liquorin electrowinning cell 42, the fresh strip liquor 46 is recycled to thesolvent extraction plant 38 for reloading.

After the copper values in the pregnant processes leach solution havebeen stripped in solvent extraction plant 38, the replenished processleach solution 48 may be recycled to the heap for another pass throughthe heap. Because most solvent extraction plants are operated at atemperature below about 50° C., the pregnant process leach solution thatis supplied to the solvent extraction plant will typically need to becooled to a temperature suitable for the solvent extraction plant. Onthe other hand, the refreshed process leach solution is preferablyheated to a temperature as close to the operating temperature of theheap prior to its reapplication to minimize the heat drains on thesystem. Thus, in a preferred method of practicing the present invention,the refreshed process leach solution 48 and pregnant process leachsolution are passed through separate sides of a heat exchanger 50 priorto delivering the collected process leach solution to the solventextraction plant. In this way, heat may be removed from the collectedpregnant process leach solution in preparation for its treatment in thesolvent extraction plant 38 and transferred to the refreshed processleach solution 48 prior to its application to the heap, thus minimizingheat losses from the system. After passing through heat exchanger 50,the process leach solution may be pumped to the top of heap 20 throughsupply line 30. Fresh water supply 52 may be used to make up for waterlosses in the system due to evaporation.

In addition to using solvent extraction to recover copper from thepregnant process leach solution, other techniques that are known in theart may also be employed, including copper cementation and ion exchange.

Ion exchange processes offer an advantage due to the fact that they canbe operated at higher temperatures than solvent extraction plants. As aresult, less heat will be lost from the system because the need to coolthe process leach solution prior to copper recovery may be effectivelyeliminated. Copper cementation offers a similar advantage. However, thepurity of copper produced through copper cementation is not as high asthat produced through solvent extraction followed by electrorefining.Furthermore, due to the fact that the copper in solution is replacedwith iron during the cementation process, the use of copper cementationwould also require frequent treatments of the process leach solution toremove excess iron concentrations to prevent excessive precipitation.

FIGS. 2A-2D schematically illustrate a manner of practicing the presentinvention over a period of time to more effectively utilize the heatvalues produced through the oxidation of the sulfide minerals in theheap. Essentially an initial heap 20 is prepared as described above.After heap 20 has reached an optimum temperature for the biooxidation ofthe hypogenic copper sulfide minerals contained therein, approximately60 to 70° C., and the oxidation of the hypogenic copper sulfides isproceeding rapidly therein, a second heap or lift 54 may be added on thetop of heap 20. The heat emitted from currently active heap 20 will helpto heat heap 54 to a temperature at which biooxidation of the hypogeniccopper sulfides within heap 54 may proceed rapidly. Again, once the hightemperature biooxidation of the hypogenic copper sulfides is proceedingrapidly in heap 54 and a substantial portion of heap 54 has reached atemperature of approximately 60 to 70° C., a third heap or lift 56 maybe constructed on top of heap 54. Again, the heat emitted from activeheap 56 will help to heat heap 56 to a temperature at which the hightemperature biooxidation of the hypogenic copper sulfides in the heapmay proceed. This process may be repeated over and over again with asmany heaps or lifts as desired. FIG. 2D, for example, illustrates afourth heap or lift 58 being constructed on top of third heap 56.

Another advantage of practicing the present invention in a series ofstacked heaps or lifts is that as the sulfide mineral fuel values in thelower heaps or lifts are depleted through the biooxidation process, thetemperature of these lower heaps will begin to drop. However, heat fromthe upper heaps or lifts will help to maintain the lower heaps at atemperature sufficient for the high temperature biooxidation ofhypogenic copper sulfides to continue for a period longer than wouldotherwise be possible. Furthermore, even if the exposed sulfide mineralvalues in the lower heaps are depleted to the point that, even with theadditional heat being supplied by the upper heaps, the heap cannotmaintain a temperature high enough for the thermophilic microorganismsto remain active, biooxidation may continue with mesophilic andthermophilic microorganisms. Moreover, the high concentrations of ferricthat are produced in the upper heaps will also aid in the continuedleaching of the copper sulfide minerals in the lower heaps or lifts.Thus by practicing the invention in a series of stacked heaps or liftsas described above, it may be possible to achieve higher overallrecoveries of copper from the ore.

The preferred embodiments of the invention having been described,various aspects of the invention are further amplified in the examplesthat follow. Such amplifications are intended to illustrate theinvention disclosed herein, and not to limit the invention to theexamples set forth. For example, the specific examples described beloware all directed to chalcopyrite bearing ores and concentrates becausethese ores and concentrates are preferred for use in practicing thepresent invention in view of the fact that chalcopyrite is economicallythe most important source of copper. However, as described above, theprocess according to the present invention may be used to bioleach alltypes of hypogenic copper sulfide bearing ores and concentrates.

EXAMPLE 1

Samples of recalcitrant chalcopyrite ore and concentrate from the SanManuel Copper Mine in Arizona were used to evaluate the use ofthermophilic microorganisms to bioleach chalcopyrite in a heap process.In order to simulate the heap leaching process, a column test wasperformed. A total of 491.2 g of smelter feed chalcopyrite concentratewere coated onto 5 Kg of ore from the same San Manuel Mine. Because theconcentrate was smelter grade, the sulfide mineral particles within theconcentrate were comprised almost entirely of chalcopyrite. Analysis ofthe smelter concentrate showed that it contained 28.5% copper and 27.5%iron and 33.6% sulfur as sulfide. Thus, without considering the exposedsulfide minerals in the coarse ore support, the concentrate coated orecontained at least 3% exposed sulfide sulfur.

The support rock that the concentrate was coated onto was prepared bysize separation of crushed San Manuel ore. The minus 19 mm crushed orewas separated into a minus 3.2 mm fraction, a 3.2 to 6.4 mm fraction anda 6.4 mm to 12.7 mm fraction and a plus 12.7 mm fraction. The 3.2 to 6.4mm and the 6.4 to 12.7 mm fractions were used in equal weights (2.5 Kgeach) as support rock for the smelter concentrate. The minus 3.2 mm andplus 12.7 mm fractions were not used in the test. Exclusion of the minus3.2 mm fraction ensured that the heap had good air flow characteristics.

Analysis of the 3.2 to 6.4 mm ore indicated that it contained 0.549%copper and 2.37% iron. Analysis of the 6.4 to 12.7 mm ore contained0.523% copper and 2.38% iron. The mixture of the two sizes ofchaleopyrite ore were coated with the high grade copper concentrate byrolling the ore in a drum at about 30 rpm while spraying with 10%sulfuric acid. After the support rock was wetted the dry concentrate wasspread over the tumbling support rock. More liquid was sprayed onto themixture until the coarse ore particles were coated with the concentrate.The final water content of the concentrate coated coarse ore particleswas approximately 3% by weight.

The mixture of concentrate and coarse ore support was then placed intoan 8.0-cm glass column to simulate a heap. The column was wrapped withelectrical resistive heating tape to insulate the column and helpcontrol temperature. The temperature was monitored by a thermocoupletaped to the outside of the glass tube and a glass thermometer in thetop of the ore at the top of the column. Air and liquid were introducedinto the top of the column. The air was heated by bubbling throughheated water and then through a heated stainless steel tube to the topof the column. Liquid was collected from the bottom of the column in aheated beaker. Air exiting the bottom of the column was bubbled throughthe liquid in the heated beaker. This was done to keep any bacteria inthe solution alive and active. The flow rate of the liquid pumped to thetop of the column was at least one liter per day. The pH of the solutionwas measured once per day and adjusted to a pH of between 1.1 and 1.3with sulfuric acid. The copper and iron levels in solution weredetermined once or twice per week. Solution was removed from the systemand replaced with new solution containing the nutrient mixture. This wasdone to keep the solution from becoming too high in copper and toxic tothe microorganisms. The liquid medium introduced to the top of thecolumn contained 0.16 g/l, NH₄Cl, 0.326 g/l Mg Cl₂ 6H₂0, 0.1 g/l K₂HPO₄, 0.1 g/l KCl, plus 1 ml/l of a trace mineral solution listed inTable 1 below. As those skilled in the art will appreciate, theconcentration of nutrients in the liquid medium were lower than thattypically found in the 9K salt generally used in connection withbiooxidation. The lower concentration of nutrients as well as thechloride medium and low pH were used to minimize the precipitation offerric as jarosite and any concomitant plugging of air or liquid flowchannels that might otherwise result. TABLE 1 Trace Mineral Solution g/lMnCl₂ × 4H₂O 1.8 Na₂B₄O₇ × 10H₂O 4.5 ZnSO₄ × 7H₂O 0.22 CuCl₂ × 2H₂O 0.05Na₂MoO_(4 ×) 2H₂O 0.03 VOSO₄ × 2H₂O 0.03 CoSO₄ 0.01

The temperature of the column was first maintained at 35° C. andinoculated on day three with 25 ml of Thiobacillus ferrooxidans, whichwere originally started with ATCC strains 19859, 14119, 23270, and 33020from the American Type Culture Collection in Rockville, Md. The bacteriaconcentration was approximately 10⁸ bacteria per ml. On day four thetemperature of the column was increased to 40° C. On day five thetemperature was increased to 45° C. On day seven the temperature wasincreased to 65° C. and reinoculated with 25 ml of a mixed culture ofThiobacillus ferrooxidans, Leptospirillum ferrooxidans, and cultures ofThiobacillus thiooxidans (ATCC strains 8085 and 15494) and a culture ofmoderate thermophiles isolated from an ore sample from the Atlanta Mineof the Ramrod Gold Co. in Idaho. On day 14 the temperature of the columnwas increased to 70° C. The column was then inoculated with a previouslyfrozen mixed culture of extreme thermophiles comprising Acidianusbrierleyi (DSM strain 1651), and Sulfolobus acidocaldarius (ATCC strains33909 and 49426). The DSM strains were obtained from the DeutscheSammlung von Mikroorganismen collection center in Braunschweig, Germany.As biooxidation within the heap had not increased as much as desiredeven though the heap was inoculated with a mixed culture of thermophileson day 14, on day 40 a fresh culture of extreme thermophiles includingAcidianus brierleyi (DSM strains 1651 and 6334) Acidianus infernus, (DSMstrain 3191) Metallosphaera sedula (ATCC strain 33909) Sulfolobusacidocaldarius (ATCC strain 49426) and Sulfolobus metallicus (DSM strain6482) d to the column. The temperature of the column and the heatedcontainer of circulating solution were maintained between 60 and 75° C.for the remainder of the 93-day experiment.

The progress of the experiment was monitored by the solubilization ofcopper. The total copper in both the concentrate and the ore support wasestimated by the analysis of a split sample of each size fraction of oresupport used and the chalcopyrite concentrate. The estimated percentagesleached for both iron and copper as the experiment progressed are listedin Table 2 and are plotted against time in FIG. 3. The concentrations ofboth iron and copper in the circulating solutions are also listed inTable 2. TABLE 2 Chalcopyrite Smelter Concentrate On Chalcopyrite OreDays Con. of Fe g/l Con. of Cu g/l Fe % leached Cu % leached 3 0.4560.508 0.66 1.13 6 2.16 0.68 0.89 2.78 12 4.856 0.56 4.89 2.46 17 4.0320.444 8.91 3.08 24 1.772 0.224 11.81 3.79 31 1.3 0.452 15.32 6.59 351.164 0.34 17.31 7.30 39 0.716 0.24 18.57 7.94 45 0.684 0.976 20.7014.51 47 0.643 1.732 21.78 20.48 51 2.26 5.84 23.60 27.53 54 1.924 5.125.21 34.12 58 1.86 4.764 26.94 40.80 60 1.352 3.48 27.81 44.23 61 0.8642.376 28.26 46.33 65 0.876 2.64 39.52 52.33 69 0.912 2.832 31.01 59.3972 0.669 1.86 32.22 64.52 76 0.62 1.512 34.03 71.23 79 0.652 1.232 35.7276.09 81 0.812 1.268 36.62 78.22 82 0.464 0.736 37.12 79.44 83 0.5840.832 37.59 80.42 86 0.924 1.228 38.66 82.57 90 0.464 0.532 39.96 84.8393 0.655 0.632 40.97 86.33

The rate of copper leaching showed a noticeable increase 16 days afterinoculation with the first culture of extreme thertophiles. The secondinoculation of extreme thermophiles increased the rate of copperleaching even more by day 47 of the experiment. The rate of leaching didnot slow down until after day 86 of the experiment when the estimatedtotal ached was 82.6%. After another week the column was taken down sothat each fraction analyzed for the extent of copper leaching.

The material in the column was separated into four size fractions. Onefraction was smaller than 0.14 mm and weighed 224.6 g. This sizefraction was considered to be the remaining chalcopyrite concentrate.Another size fraction was larger than 0.14 mm and smaller than 3.2 mmand weighed 340.8 g. This size range of material was never put into thecolumn and was believed to be the result of breakdown of the 2.5 Kg of3.2 mm to 6.4 mm ore that was put into the column at the start. Theamount of material remaining in the 3.2 mm to 6.4 mm size range was2,108 g. The weight of the remaining 6.4 mm to 12.7 mm was 2,304 g.

Analysis of each size fraction was used to calculate the extent ofchalcopyrite leaching for both the concentrate and the ore. The analysisof the 224.6 g of smelter concentrate showed 3.24% copper and 18.5% ironor a total of 7.28 g of copper and 41.6 g of iron. The original 491.2 gof copper concentrate was 28.5% copper and 27.5% iron and thereforecontained 140.0 g of copper and 135.1 g of iron. The calculatedpercentage leached was 94.8% for copper and 69.2% for iron. The estimateof copper and iron leaching of the 3.2 to 6.4 mm ore used as support wasbased on the 0.355% copper and 4.19% iron remaining in the 0.14 mm to3.2 mm size fraction and the 0.305% copper and 2.08% iron remaining inthe 3.2 mm to 6.4 mm size fraction. The total remaining copper and ironwas 7.64 g and 58.1 g, respectively. Thus, the calculated percentageleached for the original 3.2 to 6.4 mm size fraction was 44.3% forcopper and 1.8% for iron. The high level of remaining iron suggestedthat this size fraction contained some of the concentrate or containedprecipitated iron. The largest size fraction was 0.353% copper and 2.27%iron. The total remaining copper was 8.13 g and the total remaining ironwas 52.3 g out of the original 13.08 g of copper and 59.5 g of iron. Theamount of copper and iron leached for this size fraction was 37.8% and12.1%, respectively. The low level of iron removal indicated that someiron had precipitated. The calculated total copper that leached from themixture of chalcopyrite ore and concentrate was 86.2% and 401% for iron.This agreed very well with the extent of leaching estimated by analysisof the circulating solution.

EXAMPLE 2

The experiment described in Example 1 was repeated using 486.8 g of thesame smelter grade concentrate that was used in that experiment. Thesupport rock that the concentrate was coated onto comprised 2.5 Kg of3.2 mm to 6.4 mm ore and 2.5 Kg of 6.4 mm to 12.7 mm ore. The mixture ofthe two sizes of chalcopyrite ore was coated with the high-gradeconcentrate by rolling the ore in a drum at about 30 rpm, while sprayingwith water. Water was used in this experiment to show that acid could beadded later. The dry concentrate was spread over the wetted tumblingplurality of substrate ore as was done is Example 1. The final watercontent of the coated coarse ore particles was approximately 3% byweight. Furthermore, as with Example 1, without considering the exposedsulfide minerals in the coarse support, the concentrate coated orecontained approximately 3% exposed sulfide sulfur.

The concentrate coated substrates were placed into an 8.0 cm glasscolumn. The column was wrapped with electrical resistive heating tape toinsulate the column and to help control its temperature. The temperaturewas monitored by a thermocouple taped to the outside of the column and aglass thermometer placed in the center of the ore in the top of thecolumn. An additional 100 g of the uncoated mixture of ore from 3.2 mmto 12.7 mm was used to cover the concentrate coated ore material. Thisuncoated ore formed a layer about 5 cm thick that covered the coatedsubstrates and acted as an insulating layer to prevent heat loss at thetop of the bed.

Air and liquid were introduced into the top of the column as was done inExample 1. The air was heated by bubbling through heated water and aheated stainless steel tube as was done in Example 1. The liquid exitingthe column was held in a heated beaker as described in Example 1.

For the first three days the temperature of the column was maintained at35° C. while two liters of 5% sulfuric acid were circulated through thecolumn at a flow rate in excess of one liter per day. The highconcentration of acid rapidly adjusted the pH to below 1.0. On the thirdday the temperature was increased to 70° C. and the same nutrientmixture as described in Example 1 was used to replace the circulatingacid solution. After about four hours the column was inoculated with thesame culture of extreme thermophiles, namely Acidianus brierleyi (DSMstrains 1651 and 6334), Acidianus infernus (DSM strain 3191), Sulfolobusacidocaldarius (ATCC strain 49426), and Sulfolobus metallicus (DSMstrain 6482), that was used to inoculate the column of Example 1 on day40. Seven days later (day 10 from the start) the column was inoculatedwith a culture of microorganisms recovered from the take down of thecolumn in Example 1. Bacteria can be recovered after the biooxidizedconcentrate is washed from the substrate. The slurry of strippedconcentrate is allowed to settle overnight. The cloudy liquid can havehigh levels (10⁷ or more bacteria per ml) of bacteria that can be usedto inoculate directly or that can be centrifuged to form even higherconcentrations of bacteria. About one fourth the bacteria recovered thisway from the column experiment in Example 1 were used to inoculate therepeat column in this example on day 10.

After the initial treatment with 5% sulfuric acid, the pH of the processleach solution added to the top of the heap was kept between a pH of 1.1and 1.3. The pH of the off solution was generally between 1.3 and 1.6.The copper and iron levels in solution were determined once or twice aweek. Solution was removed from the system and replaced with newsolution containing the nutrient mixture. This was done for the samereason that it was in Example 1, namely to keep below the toxic level ofcopper until the microorganisms had time to adapt to high copperconcentrations.

The major difference between the experiment in Example 1 and this one isthe early use of high temperature (70° C.) and early inoculation with afresh culture of extreme thermophiles.

The extent of copper and iron leaching was estimated by determination ofthe copper and iron concentrations in solution, which are plottedagainst time in FIG. 4. The earlier start of leaching, which in thepresent example is a result of the earlier inoculation, demonstrates thebenefit of using extremely thermophilic microorganisms in leachingrecalcitrant chalcopyrite. The material from this column was separatedinto size fractions. The fraction smaller than 0.14 mm material weighed315.4 g and contained 2.74% copper and 12.7% iron by analysis. Theoriginal 486.8 g of copper concentrate contained 138.7 g of copper and133.8 g of iron. The calculated percentage leached was 93.8% for copperand 70.0% for iron. The estimate of copper and iron leaching for the0.14 to 12.7 mm ore used as support was based on the 15.36 g of copperand 78.9 g of iron remaining in this size fraction. The calculatedpercentage leached was 43.8% of the copper and 34.9% of the iron.

EXAMPLE 3

A sample of chalcopyrite concentrate from the San Manuel copper mine inArizona was used to perform a 35° C. control experiment in a similarcolumn test. A total of 391.8 g of smelter grade concentrate containing28.8% copper and 27.3% iron was coated on to a plurality of granitesupport rocks. The 3920 g of support rock that was coated had no coppermineral in it and was between 6.4 and 12.7 mm in size. The sample ofgranite support rock had a small amount of carbonate and tended to causesome precipitation of iron. The method of coating was similar to themethod used in Examples 1 and 2 with the exception that about 110 ml ofbacteria containing solution were used to wet the support rock beforeapplying the dry concentrate.

As the concentrate contained over 30% sulfide sulfur, the concentratedcoated support rock contained approximately 3% exposed sulfide sulfur.

The mixture of concentrate and coarse granite support rock were placedin a 7.6-cm plastic column. The column was wrapped with resistiveelectrical heating tape to insulate the column and to help controltemperature. In this example the temperature was maintained at 35° C.throughout the experiment. Air and liquid were introduced into the topof the column. Liquid was collected from the bottom of the column and pHadjusted before reapplying it to the top of the column. The pH of theoff solution ranged between 1.37 and 1.76 and the pH of the reappliedsolution was between 1.2 and 1.5. The copper and iron levels insolutions were determined at least once per week. Solution removed fromthe system was replaced with new pH adjust nutrient solution. The mediumcontained 1.0 g/l NH₄ SO₄; 0.2 g/l MgSO₄ 7H₂O 0.02 g/l K₂HPO₄; 0.03 g/lKCl. This experiment did not use the chloride nutrient solution used inExamples 1 and 2. The nutrient solution used in Examples 1 and 2 wasused in order to minimize the amount of iron precipitation at the higherleach temperature of 70° C.

The bacteria concentration in the solution that was used to wet thecoarse ore was approximately 10⁸ bacteria per ml and was of the samemixed culture used in the first inoculation of Example 1. On day 44, 990ml of 10.08 g/l ferric solution was added to the circulating five litersof solution to increase the iron level to approximately 2 g/l. The ironlevel had been low (less than 1 g/l) for the first 44 days. After theferric addition the iron levels remained over 1 g/l until after day 85.The copper level of the solution was maintained at above 1 g/l after thefirst 10 days.

The control experiment was conducted for 100 days. The Eh exceeded 0.6volts after 50 days. The high Eh indicated that bacteria growth andbioleaching were in progress during most of the 100-day experiment.However, only 20% of the copper was leached after 60 days, and only25.2% after 100 days. The experiment was stopped after 100 days. Thematerial from the column was separated into a minus 0.14 mm and a plus0.14 mm size fraction. Each fraction was analyzed to determine thecopper remaining in the system. The weight of the granite support rockincreased to 4087.2 g and had picked up 0.928% copper. The weight of theconcentrate had dropped to 218.6 g and the copper content was 19.4%. Thetotal copper remaining in the column after 100 days of bioleaching was80.34 g or 71.2% of the original 112.8 g. The copper analysis of thesolution estimated that 25.3% had leached out of the column. Thiscompares well with the 28.8% calculated by final copper analysis.

The extent of copper and iron leaching were estimated by determinationof the copper and iron concentrations in solution. The estimated extentof leaching for copper and iron are plotted against time in FIG. 5.

EXAMPLE 4

A concentrate was made from the minus 3.2 mm fraction of the San Manuelore. The concentrate was made by grinding the ore to pass 0.107 mm. Theground ore sample was then floated to form a sulfide concentrate. Theflotation was done in small batches of 500 g each in a laboratory Wemcoflotation cell. Before flotation, the ground ore sample was adjusted toa pulp density of 30%. Then the pH was adjusted to between 7 and 9 withNaOH. Potassium amyl xanthate was added as a collector at approximately100 g/tonne and mixed more than 5 minutes before 50 g/tonne of DowfrothD-200 was added and mixed for another 5 minutes. Finally, air wasintroduced to produce a sulfide concentrate that contained 8.5% copperand 30.4% iron and 35.8% sulfide by weight. Thus, this concentratecontained almost twice the amount by weight of pyrite as it didchalcopyrite.

A plurality of coated substrates were then made by coating 200 g of thesulfide concentrate on to 2,000 g of plus 6.2 mm minus 12.7 mm graniterock. The concentrate was added as a dry powder to the wetted supportrock in a drum rotating at about 30 rpm. The dry concentrate was spreadover the tumbling support rock. More liquid was sprayed onto the mixtureuntil the coarse support rock was coated with the concentrate. The finalwater content of the coated coarse ore particles was approximately 3% byweight. Furthermore, the concentrate coated ore contained approximately3.2% exposed sulfide sulfur.

The plurality of coated substrates were then put into a 5 cm glasscolumn. The column was wrapped with electrical resistive heating tape toinsulate the column and help control temperature. The temperature wasmonitored by a thermocouple taped to the outside of glass tube and by aglass thermometer placed in the center top of the column. Air and liquidwere introduced into the top of the column. The air was passed throughheated water before entering the column. Liquid was collected from thebottom of the column but was not heated as it was in Example 1.

The flow rate of liquid pumped to the top of the column was at least 0.5liters per day. The pH of the solution was measured once per day andadjusted to a pH between 1.1 and 1.3. The first solution used in thisexperiment was a different chloride nutrient mixture than used inExample 1 above. In this experiment the first nutrient solutioncomprised 2.03 g/l NH₄Cl; 0.08 g/l KCl; 0.04 g/lK₂HPO₄; 0.35 g/lMgCl6H₂O. On day four this was replaced with a solution that was thesame except that it also contained 2 g/l ferric made with ferricsulfate. This solution was again removed and replaced on day seven. Thenew solution also contained 2 g/l ferric. On day 29 the solution waschanged again and replaced with the chloride nutrient solutioncontaining 2 g/l ferric. This solution was recirculated until day 63when one liter out of the two liters in the beaker was replaced withfresh chloride nutrient solution. Another liter was removed and replacedon day 65 with the chloride nutrient solution. No ferric was added tothe solution on days 63 and 65. One liter of solution was replaced withfresh chloride nutrient solution on days 74, 77, 81, 84 and 91. Thecolumn experiment was stopped after day 93. The bioleached material fromthe column was separated into a minus 0.14 mm size fraction and plus0.14 mm fraction. Each size fraction was analyzed for copper, iron, andsulfide.

The temperature of the column was first maintained at 35° C. andinoculated with the same bacteria culture as used to initially inoculatethe column in Example 1. On day seven the temperature was increased to40° C. and reinoculated with the same mesophilic culture. The next daythe temperature was increased to 45° C. and the column inoculated with amoderate thermophiles isolated from an ore sample from the Atlanta mineof Ramrod Gold in Idaho. On day 10 the temperature was increased to 60°C. On day 11, 25 ml (10⁸ bacteria per ml) of the same culture ofmesophilic bacteria were added to the unheated off solution beaker. Thebeaker was reinoculated with 25 ml of 10⁸ bacteria per ml on days 13 and15. On day 18, the column was inoculated with the same previously frozenmixed culture of extreme thermophiles as was used to inoculate thecolumn in Example 1 on day 14. The off solution beaker was furtherinoculated on day 30 and day 45 with mesophilic bacteria. This columnexperiment was never inoculated with the fresh culture of extremethermophiles used in Example 1 at day 40. A plot of the estimatedpercentage of copper and iron leached is plotted against time in FIG. 6.The use of the granite rock as support may have caused excessiveprecipitation of iron, due to its carbonate content. The estimatedpercentage iron leaching did not go above zero until after day 60. Thisprecipitation could have limited the extent of copper leaching in thisexperiment also. One benefit of having no iron leach during the process,however, is that a purer pregnant leach liquor is produced for thesolvent extraction plant.

The final analysis of copper indicated that 82.5% of the copper had beenleached from the concentrate. The amount of copper remaining in the 276g of the minus 0.14 mm material was 0.916%. The weight of theconcentrate had increased from precipitation and loss of support rock,During the experiment the 2,000 g of granite support rock lost 140.8 g.

Analysis showed that 28.7% of the iron was removed and that 45.2% of thesulfide sulfur was biooxidized. Microscopic analysis of the water usedto wash the coated concentrate off the support rock showed a largenumber (over 10⁷ microorganisms per ml) of extreme thermophiles.

EXAMPLE 5

Another column experiment was carried out at the same time as theexperiment described in Example 4. This experiment was the same with oneexception. The difference was that 10 g of finely powdered graphite wasmixed with 200 g of bulk flotation concentrate. This was the sameconcentrate used in Example 4, and the column was set up the same way asin Example 4. The inoculations and pH adjustments were also the same asin Example 4.

The estimated percentage of copper and iron leached is plotted againsttime in FIG. 7 for this example.

The column experiment was continued for 93 days. The results of thiscolumn experiment indicated 89.8% copper leaching by analysis of offsolution and 89.0% by analysis of the material removed from the column.Iron leaching was also low in this experiment and was also believed tobe due to precipitation caused by the carbonate in the granite support.Analysis for iron and sulfide sulfur indicated 18.6% iron removal and53.9% sulfide biooxidation.

The graphite was added to enhance the galvanic connection betweenchalcopyrite and pyrite in the concentrate.

EXAMPLE 6

The experiment described in Example 1 was repeated using 491.8 g of thesame smelter grade concentrate that was used in that experiment. Thesupport rock that the concentrate was coated onto comprised 2.5 Kg of3.2 mm to 6.4 mm coarse ore and 2.5 Kg of 6.4 mm to 12.7 mm coarse ore.The mixture of the two sizes of chalcopyrite ore were coated with thehigh grade concentrate by rolling the ore in a drum at about 30 rpm,while spraying with 10% H₂SO₄ as was used in Example 1. The dryconcentrate was spread over the wetted tumbling plurality of oresubstrates as was done is Example 1.

The coated substrates were placed into an 8.0-cm glass column. Thecolumn was wrapped with electrical resistive heating tape to insulatethe column and help control the temperature. The temperature wasmonitored by a thermocouple taped to the outside of the column and aglass thermometer in the center top of ore in the column. An additional100 g of the uncoated ore from 6.4 mm to 12.7 mm was used to cover thecoated ore material. This uncoated ore formed a layer about 2 cm thickthat covered the coated substrate and acted as an insulating layer toprevent heat loss at the top of the bed.

Air and liquid were introduced into the top of the column as was done inExample 1. The air was heated by bubbling through heated water and aheated stainless steel tube as was done in Example 1. The liquid exitingthe column was held in a heated beaker as described in Example 1.

From the first day the temperature of the column was maintained at 70°C. while four liters of a solution having a pH of 1.0 were circulatedthrough the column at a flow rate in excess of one liter per day. Thesolution used in connection with this example was different than it wasin Examples 1 and 2. This media used in this example comprised 0.2 g/l(NH₄)₂SO₄, 0.4 g/l MgSO₄-7H₂O, 0.1 g/l K₂HPO₄, 0.1 g/l KCl. The highconcentration of acid used to coat coarse ore support rapidly adjustedthe pH of the coated ore to below 1.6. On the second day the column wasinoculated with the same culture of extreme thermophiles (Acidianusbrierleyi (DSM strains 1651 and 6334), Acidianus infernus (DSM strain3191), Sulfolobus acidocaldarius (ATCC strain 49426), and Sulfolobusmetallicus (DSM strain 6482)) that was used to inoculate the column ofExample 2. This mixed culture of extreme thermophiles was recovered fromthe take down of the column in Example 1. Bacteria can be recoveredafter the biooxidized concentrate is washed from the support material.The slurry of stripped concentrate is allowed to settle overnight. Thecloudy liquid can have high levels (10⁷ or more bacteria per ml) ofbacteria that can be used to inoculate directly or that can becentrifuged to form higher concentrations of bacteria.

The pH of the process leach solution added to the top of the column waskept between a pH of 1.1 and 1.3. The pH of the off solution wasgenerally between 1.3 and 1.6. The copper and iron levels in solutionwere determined once or twice a week. Solution was removed from thesystem and replaced with new solution containing the nutrient mixture.This was done for the same reason as it was in Example 1, namely to keepbelow the toxic level of copper until the microorganisms had time toadapt to high copper concentrations.

The major difference between the experiments in Examples 1 and 2 and thepresent one is the use of a sulfate media to which no chloride had beenadded.

The extent of copper and iron leaching was estimated by determination ofthe copper and iron concentrations in the off solution, and are plottedagainst time in FIG. 8.

EXAMPLE 7

Another concentrate was made from the minus 3.2 mm fraction of SanManuel ore. The same procedure was used as was described in Example 4.This bulk pyrite-chalcopyrite concentrate was 7.3% copper, 27.4% iron,and over 30% sulfide sulfur. Thus, this concentrate containedapproximately twice the amount by weight of pyrite as it didchalcopyrite. Unlike Example 4, the 443.1 g of this concentrate werecoated onto chalcopyrite ore that comprised 2.5 Kg of 3.2 mm to 6.4 mmore and 2.5 Kg of 6.4 mm to 12.7 mm ore. The mixture of the two sizes ofchalcopyrite ore were coated with the low grade concentrate by rollingthe ore in a drum at about 30 rpm, while spraying with 10% H₂SO₄ as wasused in this Example 1. The dry concentrate was spread over the wettedtumbling plurality of coarse ore substrates as was done in Example 1.The final water content of the coated coarse ore particles wasapproximately 3% by weight. Furthermore, without considering the exposedsulfide mineral particles in the ore support material, the concentratecoated ore contained approximately 2.5% exposed sulfide sulfur.

Because the chalcopyrite concentrate was lower grade than in theprevious examples, the amount of copper that was in the concentrate wasabout the same as the amount of copper that was in the ore support rock(54.2% of the copper was in the coated concentrate and 45.8% was in theore support rock).

The coated substrates were placed into an 8.0-cm glass column. Thecolumn was wrapped with electrical resistive heating tape to insulatethe column and help control the temperature. The temperature wasmonitored by a thermocouple taped to the outside of the column and aglass thermometer placed in the center of the ore in top of the column.An additional 100 g of the uncoated ore from the 6.4 mm to 12.7 mmfraction was used to cover the coated ore material. This uncoated oreformed a layer about 2 cm thick that covered the coated substrate andacted as an insulating layer to prevent heat loss at the top of the bed.

Air and liquid were introduced into the top of the column as was done inExample 1. The air was heated by bubbling through heated water and aheated stainless steel tube as was done in Example 1. The liquid exitingthe column was held in a heated beaker as described in Example 1.

From the first day the temperature of the column was maintained at 70°C. while four liters of solution having a pH of 1.0 were circulatedthrough the column at a flow rate in excess of one liter per day. Inthis example the solution was the same as it was in Examples 1 and 2.The media comprised 0.16 g/l NH₄Cl, 0.326 g/l MgCl-6H₂O, 0.1 g/l K₂HPO₄,and 0.1 g/l KCl. The high concentration of acid used to coat theconcentrate on the ore support rapidly adjusted the pH to below 1.8. Onthe second day the column was inoculated with the same culture ofextreme thermophiles (Acidianus brierleyi (DSM strains 1651 and 6334),Acidianus infernus, (DSM strain 3191), Sulfolobus acidocaldarius (ATCCstrain 49426), and Sulfolobus metallicus (DSM strain 6482)) that wasused to inoculate the column of Example 2. This mixed culture of extremethermophiles was recovered from the take down of the column inExample 1. Bacteria can be recovered after the biooxidized concentrateis washed from the substrate. The slurry of stripped concentrate isallowed to settle overnight. The cloudy liquid can have high levels (10⁷or more bacteria per ml) of bacteria that can be used to inoculatedirectly or that can be centrifuged to form higher concentrations ofbacteria.

The pH of the process leach solution applied to the top of the columnwas kept between a pH of 1.1 and 1.3. The pH of the off solution wasgenerally between 1.3 and 1.6. The copper and iron levels in solutionwere determined once or twice a week. Solution was removed from thesystem and replaced with new solution containing the nutrient mixture.This was done for the same reason as it was in Example 1, namely to keepbelow the toxic level of copper until the microorganisms had time toadapt to high copper concentrations.

The major difference between the experiments in Examples 1 and 2 and thepresent one is the use of a low-grade bulk pyrite-chalcopyriteconcentrate. The presence of pyrite can increase the rate ofchalcopyrite leaching by galvanic interaction. This example is alsodifferent than Examples 4 and 5 because bioleaching was done at 70° C.from the start and the heap was inoculated with the same culture ofextreme thermophiles as used in Examples 1, 2, and 6.

The extent of copper and iron leaching was estimated by a determinationof the copper and iron concentrations in solution, and are plottedagainst time in FIG. 9. The copper leaching slowed after leaching theequivalent of the amount of copper that was estimated to be containedwithin the bulk concentrate coated on the ore. This was 54.2% of thetotal copper in the column and was leached before day 40 of theexperiment. The remaining copper, believed to be from the support copperore leached at a slower rate from day 40 on.

Although the invention has been described with reference to preferredembodiments and specific examples, those of ordinary skill in the artwill readily appreciate that many modifications and adaptations of theinvention are possible without departure from the spirit and scope ofthe invention as claimed hereinafter.

1. A high temperature heap bioleaching process, the process comprisingthe steps of: a. constructing a heap comprising hypogenic copper sulfidebearing ore, said heap including exposed sulfide mineral particles atleast 25 weight % of which comprise hypogenic copper sulfides, whereinthe concentration of exposed sulfide mineral particles in said heap issuch that said heap contains at least 10 Kg of exposed sulfide sulfurper tonne of solids in said heaps and wherein at least 50% of the totalcopper in said heap is in the form of hypogenic copper sulfides; b.heating at least 50% of said heap to a temperature of at least 60° C.;c. maintaining at least 50% of said heap at a temperature of at least60° C. until at least 50% of the copper in said heap is dissolved; d.inoculating said heap with a culture comprising at least onethermophilic microorganism that bioleaches sulfide minerals at atemperature above 60° C.; and e. bioleaching sufficient sulfide mineralparticles in said heap to oxidize at least 10 Kg of sulfide sulfur pertonne of solids in said heap and to cause the dissolution of at least50% of the copper in said heap within a period of about 210 days or lessfrom completion of said heap.
 2. A high temperature heap bioleachingprocess, the process comprising the steps of; a. constructing a heapcomprising hypogenic copper sulfide bearing ore, said heap includingexposed sulfide mineral particles at least 25 weight % of which comprisehypogenic copper sulfides, wherein the concentration of exposed sulfidemineral particles in said heap is such that said heap contains at least10 Kg of exposed sulfide sulfur per tonne of solids in said heap, andwherein at least 50% of the total copper in said heap is in the form ofhypogenic copper sulfides; b. heating a substantial portion of said heapto a temperature of at least 50° C.; c. inoculating said heap with aculture comprising at least one thermophilic microorganism thatbiooxidizes sulfide minerals at a temperature above 50° C.; and d.bioleaching sulfide mineral particles in said heap to thereby cause thedissolution of the sulfide mineral particles and generate heat, whereinsufficient sulfide minerals are oxidized in a bioleaching period of 210days or less to oxidize at least 10 Kg of sulfide sulfur per tonne ofsolids in said heap and cause the dissolution of at least 50% of thecopper in said heap into a process leach solution.
 3. A high temperatureheap bioleaching process, the process comprising the steps of: a.constructing a heap comprising chalcopyrite bearing ore, said heapincluding exposed sulfide mineral particles at least 25 weight % ofwhich comprise chalcopyrite, wherein the concentration of exposedsulfide mineral particles in said heap is such that said heap containsat least 10 Kg of exposed sulfide sulfur per tonne of solids in saidheap, and wherein at least 50% of the total copper in said heap is inthe form of chalcopyrite; b. heating at least 50% of said heap to atemperature of at least 60° C.; c. maintaining at least 50% of said heapat a temperature of at least 60° C. until at least 50% of the copper insaid heap is dissolved; d. inoculating said heap with a culturecomprising at least one thermophilic microorganism capable ofbioleaching sulfide minerals at a temperature above 60° C.; and e.bioleaching sufficient sulfide mineral particles in said heap to oxidizeat least 10 Kg of sulfide sulfur per tonne of solids in said heap and tocause the dissolution of at least 50% of the copper in said heap withina period of about 210 days or less from completion of said heap.